Conventionally, map data formatted for use in a vehicular apparatus is known. Further, map data having a KIWI format is also well-known (Refer to non-patent documents 1 to 3.). The map data format uses links and nodes for representing roads, and attributes (i.e., features) for each of the links, such as link shapes, street addresses and the like, are stored in the map data as attribute data. In the following, a group of attribute data corresponding to one of those links are denoted as a link data. Conventionally, data regarding the links has been stored in the map data.
In addition, in the conventional map data, a unique link ID is assigned to each of those links. The link ID is used for association of link data corresponding to the unique link ID with other data. For example, the link ID is used to represent the connection relationships between two or more links. In the conventional map data, a plural number of link data are combined to form link series data, which includes node data regarding a node that connects two or more links by using link IDs, for ultimately representing connection relationships between two or more links.
Non-patent document 1: “Car navigation system—Public data structure KIWI and its use” by Shigeru Kakumoto, Kyoritsu publishing, February 2003
Non-patent document 2: “Road vehicles—Map data physical storage format for car navigation systems (JIS D 810:2004)” by Japanese Industrial Standard, March 2004
Non-patent document 3: “Car navigation map data format KIWI” by Hidetoshi Fujimoto, DENSO Technical Review 2001 Vol. 6, No. 1, pp 29-34
In the conventional map data structure, for each of the links, in order to hold the above-described link data that is made by grouping plural kinds of attribute data, a problem of heavy processing and editing load for editing the map data and for editing a map data retrieval program has been caused, when the attribute data of unnecessary kind is deleted from the link data, or when the attribute data of new kind is added to the link data, for the purpose of changing the contents of the map data.
For example, when new data (e.g., attribute data of new kind) is added link data to expand the link data in the conventional map data format, the new data is added to multiple places in the map data in a scattered manner, thereby drastically changing the structure of the map data as a whole. Therefore, in the conventional data format, load for changing the contents of the map data was heavy. If, on the other hand, a redundant map data area is prepared in the map data as a work-around of the above situation, the size of the map data has become unnecessarily large